We do not inherit the Earth from our ancestors; we borrow it from our children.

— American Indian proverb

Thomas Jefferson favored the notion that extinction couldn’t be part of the natural order.

“Such is the economy of nature,” he wrote, “that no instance can be produced of her having permitted any one race of her animals to become extinct; of her having formed any link in her great work so weak as to be broken.”

That conviction led Jefferson, as president, to instruct Meriwether Lewis and William Clark to be on the lookout for an American elephant during their famous 1804-05 expedition to the Northwest.

Today, paleontologists accept that normal extinctions are relatively rare in the natural world. For example, a mammal species might vanish every 700 years or so, given ordinary conditions. It follows that Jefferson and his contemporaries, living in ordinary times, might arrive at the mistaken belief that animal species simply do not disappear.

The impetus for Jefferson’s pachyderm watch was the discovery in 1739 of teeth, tusks and enormous skeletal bones along the Ohio River by members of a French, Algonquin and Iroquois military expedition led by Charles Le Moyne. The discovery site, about a half-hour’s drive southwest of Cincinnati, is known today as Big Bone Lick State Park in Kentucky.

Some of the original big bones eventually landed in the Museum of Natural History in Paris. There they were examined by paleontologist Georges Cuvier, whose conclusions would have challenged Jefferson’s belief had the soon-to-be president known of them.

Cuvier compared the fossil remains with others found in Siberia and with skeletal parts from Asian and African elephants. He declared during a public lecture in 1796 that bones showed Asian and African elephants to be distinct species. Further, the bones from Siberia and the Ohio Valley were enough unlike each other and unlike the bones of modern elephants to each represent distinct species.

In addition, the ancient bones came from species that were “lost,” Cuvier said — extinct, as they are labeled today. Cuvier’s declaration that species could disappear was revolutionary and largely unwelcome, even among scientists.

Nonetheless, people alive during Jefferson’s time would witness what the brilliant Virginian thought unlikely: the breaking of links in nature’s great works. During the decades after Jefferson’s death on July 4, 1826, lost in North America would be the red elk, the Eastern cougar, the Carolina parakeet, the passenger pigeon, the California golden bear, the heath hen and scores of other birds, mammals, fish and amphibians.

A few famed species, including the California condor and the whooping crane, are hanging on only because of herculean human efforts.

Marked by painstaking research and elegant, compelling storytelling by author Elizabeth Kolbert, The Sixth Extinction: An Unnatural History covers much ground scientific, temporal, geographical and ideological. The roles of Jefferson, Cuvier and Le Moyne help plot the direction of a sobering saga about what increasingly is being called the Anthropocene Period of Earth’s history.

Anthropocene describes an epoch shaped by the overwhelming presence and activities of human beings, more than 7 billion in number and climbing.

The era has brought the unleashing into atmosphere and ocean of carbon from fossil fuels long bound up in rock and soil. The release is warming the planet and acidifying the seas. The era has produced the destruction of wildlife habitat in order to grow crops, to expand cities and to extract the natural resources that keep a vast industrial machine stoked. Aquifers, lakes and rivers across the globe are being pumped dry.

Transportation and commerce are moving species from niches where they evolved in a kind of harmony to enemy-free environs where they can outcompete and destroy natives. In the opening pages of her book, published in March and available in paperback and as an ebook, Kolbert poignantly describes efforts to save the dying frogs of Central America, tracing their demise to a fungus spread by humans that is killing amphibians worldwide.

A fungus spread by humans is behind a disease that has killed millions of bats in North America.

Bats, frogs, toads and salamanders are only a few of the organisms threatened by what humans have wrought. Trees, including the ashes of Ohio along with the elms and chestnuts before them, have succumbed to what humans casually disperse and displace, mostly in the pursuit of wealth but also of pleasure.

The trajectory continues.

The cost, though, might be very high as species begin to die off at an increasing rate. Depending on who is doing the estimating, between 16 percent and 33 percent of vertebrates worldwide already are at risk.

Five mass extinctions have taken place during the planet’s life history. After each of the five, waves of existing plants and animals were wiped out and the order of life was changed. The most recent happened 65 million years ago, when the explosion of a huge meteorite helped usher out the age of dinosaurs and usher in the ascendance of mammals, leading after millions of years to the age of Homo sapiens that shakily began about 200,000 years ago.

Kolbert is not a lone voice, easily dismissed, warning about a Hollywood doomsday. Only last week, a scientific study led by Stanford biology professor Rodolfo Dirzo and published in the journal Science concluded that the planet appears to be heading toward a sixth mass extinction, for which humans are responsible.